The apps underestimated the calories in a meal by roughly 250 to 345 calories on average, according to research presented at NUTRITION 2026, the American Society for Nutrition's annual meeting. estimated higher calorie meals more accurately than lower calorie ones. Calorie tracking is a useful tool for many people and a harmful one for some. The confirmed finding is that four widely used photo-based apps underestimated calories and fat by about a third against meals of known composition. All four underestimated calories and fat.